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 //FJSTARTHEADER
 // $Id$
 //
 // Copyright (c) 2005-2021, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
 //
 //----------------------------------------------------------------------
 // This file is part of FastJet.
 //
 //  FastJet is free software; you can redistribute it and/or modify
 //  it under the terms of the GNU General Public License as published by
 //  the Free Software Foundation; either version 2 of the License, or
 //  (at your option) any later version.
 //
 //  The algorithms that underlie FastJet have required considerable
 //  development. They are described in the original FastJet paper,
 //  hep-ph/0512210 and in the manual, arXiv:1111.6097. If you use
 //  FastJet as part of work towards a scientific publication, please
 //  quote the version you use and include a citation to the manual and
 //  optionally also to hep-ph/0512210.
 //
 //  FastJet is distributed in the hope that it will be useful,
 //  but WITHOUT ANY WARRANTY; without even the implied warranty of
 //  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 //  GNU General Public License for more details.
 //
 //  You should have received a copy of the GNU General Public License
 //  along with FastJet. If not, see <http://www.gnu.org/licenses/>.
 //----------------------------------------------------------------------
 //FJENDHEADER
 
 #ifndef __CASUBJET_TAGGER_HH__
 #define __CASUBJET_TAGGER_HH__
 
 #include "fastjet/PseudoJet.hh"
 #include "fastjet/WrappedStructure.hh"
 #include "fastjet/tools/Transformer.hh"
 #include "fastjet/LimitedWarning.hh"
 
 FASTJET_BEGIN_NAMESPACE
 
 class CASubJetTagger;
 class CASubJetTaggerStructure;
 
 //----------------------------------------------------------------------
 /// @ingroup tools_taggers
 /// \class CASubJetTagger
 /// clean (almost parameter-free) tagger searching for the element in
 /// the clustering history that maximises a chosen distance
 ///
 /// class to help us get a clean (almost parameter-free) handle on
 /// substructure inside a C/A jet. It follows the logic described in
 /// arXiv:0906.0728 (and is inspired by the original Cambridge
 /// algorithm paper in its use of separate angular and dimensionful
 /// distances), but provides some extra flexibility.
 ///
 /// It searches for all splittings that pass a symmetry cut (zcut) and
 /// then selects the one with the largest auxiliary scale choice
 /// (e.g. jade distance of the splitting, kt distance of the
 /// splitting, etc.)
 ///
 /// By default, the zcut is calculated from the fraction of the child
 /// pt carried by the parent jet. If one calls set_absolute_z_cut the
 /// fraction of transverse momentum will be computed wrt the original
 /// jet.
 ///
 /// original code copyright (C) 2009 by Gavin Salam, released under
 /// the GPL.
 ///
 /// \section desc Options
 /// 
 ///  - the distance choice: options are
 ///        kt2_distance        : usual min(kti^2,ktj^2)DeltaR_{ij}^2
 ///        jade_distance       : kti . ktj DeltaR_{ij}^2 (LI version of jade)
 ///        jade2_distance      : kti . ktj DeltaR_{ij}^4 (LI version of jade * DR^2)
 ///        plain_distance      :           DeltaR_{ij}^2
 ///        mass_drop_distance  : m_jet - max(m_parent1,m_parent2)
 ///        dot_product_distance: parent1.parent2
 ///    (kt2_distance by default)
 ///
 ///  - the z cut (0 by default)
 ///
 ///  - by calling set_absolute_z_cut(), one can ask that the pt
 ///    fraction if calculated wrt the original jet
 ///
 ///  - by calling set_dr_min(drmin), one can ask that only the
 ///    recombinations where the 2 objects are (geometrically) distant
 ///    by at least drmin are kept in the maximisation.
 ///
 /// \section input Input conditions
 /// 
 ///  - the jet must have been obtained from a Cambridge/Aachen cluster
 ///    sequence
 ///
 /// \section output Output/structure
 /// 
 ///  - the element of the cluster sequence maximising the requested
 ///    distance (and satisfying the zcut) is returned.
 ///
 ///  - if the original jet has no parents, it will be returned
 ///
 ///  - the value of the "z" and distance corresponding to that history
 ///    element are stored and accessible through
 ///      result.structure_of<CASubJetTagger>().z();
 ///      result.structure_of<CASubJetTagger>().distance();
 ///
 class CASubJetTagger : public Transformer {
 public:
 
   /// the available choices of auxiliary scale with respect to which
   /// to order the splittings
   enum ScaleChoice {
     kt2_distance,        //< usual min(kti^2,ktj^2)DeltaR_{ij}^2
     jade_distance,       //< kti . ktj DeltaR_{ij}^2 (LI version of jade)
     jade2_distance,      //< kti . ktj DeltaR_{ij}^4 (LI version of jade * DR^2)
     plain_distance,      //<           DeltaR_{ij}^2
     mass_drop_distance,  //<    m_jet - max(m_parent1,m_parent2)
     dot_product_distance //<  parent1.parent2
   };
 
   /// just constructs
   CASubJetTagger(ScaleChoice scale_choice = jade_distance,
                  double      z_threshold  = 0.1)
     : _scale_choice(scale_choice), _z_threshold(z_threshold),
       _dr2_min(0.0), _absolute_z_cut(false){};
 
   /// sets a minimum delta R below which spliting will be ignored
   /// (only relevant if set prior to calling run())
   void set_dr_min(double drmin) {_dr2_min = drmin*drmin;}
 
   /// returns a textual description of the tagger
   virtual std::string description() const;
 
   /// If (abs_z_cut) is set to false (the default) then for a
   /// splitting to be considered, each subjet must satisfy 
   /// 
   ///        p_{t,sub} > z_threshold * p_{t,parent}
   ///
   /// whereas if it is set to true, then each subject must satisfy
   ///
   ///        p_{t,sub} > z_threshold * p_{t,original-jet}
   ///
   /// where parent is the immediate parent of the splitting, and
   /// original jet is the one supplied to the run() function.
   ///
   /// Only relevant is called prior to run().
   void set_absolute_z_cut(bool abs_z_cut=true) {_absolute_z_cut = abs_z_cut;}
   
   /// runs the tagger on the given jet and
   /// returns the tagged PseudoJet if successful, or a PseudoJet==0 otherwise
   /// (standard access is through operator()).
   virtual PseudoJet result(const PseudoJet & jet) const;
 
   /// the type of Structure returned
   typedef CASubJetTaggerStructure StructureType;
 
 protected:
   /// class that contains the result internally
   class JetAux {
   public:
     PseudoJet jet;          //< the subjet (immediate parent of splitting)
     double    aux_distance; //< the auxiliary distance between its two subjets
     double    delta_r;      //< the angular distance between its two subjets
     double    z;            //< the transverse momentum fraction
   };
 
 
   void _recurse_through_jet(const PseudoJet & current_jet, 
                             JetAux &aux_max,
                             const PseudoJet & original_jet) const;
 
   ScaleChoice _scale_choice;
   double      _z_threshold;
   double      _dr2_min;
   bool        _absolute_z_cut;
 
   static  LimitedWarning _non_ca_warnings;
 };
 
 
 //------------------------------------------------------------------------
 /// @ingroup tools_taggers
 /// the structure returned by a CASubJetTagger
 ///
 /// Since this is directly an element of the ClusterSequence, we keep
 /// basically the original ClusterSequenceStructure (wrapped for
 /// memory-management reasons) and add information about the pt
 /// fraction and distance of the subjet structure
 class CASubJetTaggerStructure : public WrappedStructure{
 public:
   /// default ctor
   ///  \param result_jet   the jet for which we have to keep the
   ///                      structure
   CASubJetTaggerStructure(const PseudoJet & result_jet)
     : WrappedStructure(result_jet.structure_shared_ptr()){}
 
   /// returns the scale choice asked for the maximisation
   CASubJetTagger::ScaleChoice scale_choice() const {return _scale_choice;}
 
   /// returns the value of the distance measure (corresponding to
   /// ScaleChoice) for this jet's splitting
   double distance() const {return _distance;}
 
   /// returns the pt fraction contained by the softer of the two component
   /// pieces of this jet (normalised relative to this jet)
   double z() const {return _z;}
 
   /// returns the pt fraction contained by the softer of the two component
   /// pieces of this jet (normalised relative to the original jet)
   bool absolute_z() const {return _absolute_z;}
 
 //  /// returns the original jet (before tagging)
 //  const PseudoJet & original() const {return _original_jet;}
 
 protected:
   CASubJetTagger::ScaleChoice _scale_choice; ///< the user scale choice 
   double _distance;  ///< the maximal distance associated with the result
   bool _absolute_z;  ///< whether z is computed wrt to the original jet or not
   double _z;         ///< the transverse momentum fraction
 //  PseudoJet _original_jet;  ///< the original jet (before tagging)
 
   friend class CASubJetTagger; ///< to allow setting the internal information
 };
 
 FASTJET_END_NAMESPACE
 
 #endif // __CASUBJET_HH__

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